Language universals are statements that are true of all languages, for example: “all languages have stop consonants”. But beneath this simple definition lurks deep ambiguity, and this triggers misunderstanding in both interdisciplinary discourse and within linguistics itself. A core dimension of the ambiguity is captured by the opposition “absolute vs. statistical universal”, although the literature uses these terms in varied ways. Many textbooks draw the boundary between absolute and statistical according to whether a sample of languages contains exceptions to a universal. But the notion of an exception-free sample is not very revealing even if the sample contained all known languages: there is always a chance that an as yet undescribed language, or an unknown language from the past or future, will provide an exception.

Sino-Tibetan is a prime example of how strongly a language family can typologically diversify under the pressure of areal spread features (Matisoff 1991, 1999). One of the manifestation of this is the average length of prosodic words. In Southeast Asia, prosodic words tend to average on one or one-and-a-half syllables. In the Himalayas, by contrast, it is not uncommon to encounter prosodic words containing five to ten syllables. The following pair of examples illustrates this.

In the late seventies, Bernard Comrie was one of the first linguists to explore the effects of the referential hierarchy (RH) on the distribution of grammatical relations (GRs). The referential hierarchy is also known in the literature as the animacy, empathy or indexibability hierarchy and ranks speech act participants (i.e. first and second person) above third persons, animates above inanimates, or more topical referents above less topical referents. Depending on the language, the hierarchy is sometimes extended by analogy to rankings of possessors above possessees, singulars above plurals, or other notions. In his 1981 textbook, Comrie analyzed RH effects as explaining (a) differential case (or adposition) marking of transitive subject ("A") noun phrases in low RH positions (e.g. inanimate or third person) and of object ("P") noun phrases in high RH positions (e.g. animate or first or second person), and (b) hierarchical verb agreement coupled with a direct vs. inverse distinction, as in Algonquian (Comrie 1981: Chapter 6).